Control apparatus for refrigeration system



June 18, 1963 w. w. LIEBRECHT 3,093,977

' CONTROL APPARATUS FOR REFRIGERATION SYSTEM Filed Sept. 15, 1961THERMOSTAT S RESEg' I12 SWIT H 00 2| CONDENSER MOTOR COMPRESSOR RR NTOVERLOAD SWIT PRESSURE PUT SWITCH LOW PRESSURE OUT SWITCH 3 2 INVEN'TOR.

Wamtmz WZIEBRECHT www ATTORNEY United States Patent 3,093,977 CONTROLAPPARATUS FOR REFRIGERATION SYSTEM Waldemar W. Liehrecht, Emerson,N..l., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis,Minn, a corporation of Delaware Filed Sept. 13, 1961, Ser. No. 137,810 4Claims. (62-208) The present invention is concerned with tan improvementin an air conditioning control system; in particular, the improvement isin the con-trol circuit for the refrigeration apparatus to provideremote manual reset of overload or high pressure lock out.

With the popularity of air conditioning, there have been manyimprovements in airconditioning installations to provide more improvedair conditioning. One of the problems faced with residential airconditioning is the noise of the motor compressor. To cut down theamount of noise in the home, the motor compressor and condenser with thecondenser fan have often been placed outdoors. In addition, air cooledcondenser systems are usually most economically installed with thecompressor and high side located outdoors. When this refrigerationapparatus is outdoors exposed to colder temperatures, compressorslugging, which is a result of the migration of the refrigerant in thesystem to the cold compressor, may occur and causes numerous problems.One method to overcome the compressor slugging is in the use of apump-down system which has a valve in the refrigerant line near theevaporator. The valve is controlled by a space thermostat in the home.The motor driven compressor is controlled from a low-pressure switch inthe refrigeration line to maintain the pressure :on the down stream sideof the compressor at some low value. When the space thermostat issatisfied, and the valve in the refrigeration line closes, the motorcompressor will operate until the pressure in the suction line isreduced to the low value. Also the compressor may start at any time tomaintain the low pressure which may be depleted by the valve leakage.

To control such a remote pump-down motor driven comppressorrefrigeration unit with a safety circuit which is commonly known as thehigh impedance reset circuit, the resetting operation of the highimpedance circuit can not be done directly from the space thermostat asthe space thermostat does not have direct control over the energizationcircuit for the motor compressor control relay.

The present invention is concerned with a specific improvement to thehigh impedanw reset circuit to provide for remote reset whenever thecircuit of the high impedance relay is momentarily broken.

An object of the present invention is to provide an improved airconditioning control circuit wherein a resetting action is obtained by aswitch means which momentarily breaks a resetting circuit.

Another object of the present invention is to provide an improvement inthe high impedance reset circuit when the circuit is used with a remotepump-down motor compressor unit so a resetting action of the controlcircuit can be obtained from a remote switch; however, the controlcircuit and pump-down function will not be inoperative if an open orshort exists in the circuit of the remote reset switch or if the manualreset switch is left in either the open or closed position.

These and other objects of the present invention will become apparentupon the study of the following specification and drawings of whichFIGURE 1 is a schematic representation of a typical air conditioninginstallation with the improved control circuit.

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FIGURE 2 is a portion of the complete control circuit to more clearlyillustrate the operation of the present invention.

Referring to FIGURE 1, a space 10 is adapted to be air conditioned. Theair from the space is circulated through an evaporator or cooling coil:11 by a fan 12 by passing into a return duct 13 and exhausting into thespace by a supply duct 14. A motor 15- which is connected to a source ofelectrical power drives fan 12.

Mounted outside the building containing space 10 is a remote air cooledpump down motor driven refrigeration apparatus 21. The refrigerationapparatus is generally located with respect to space 10 in a manner tocut down noise which might be developed by apparatus 21. The apparatusis also generally located outdoors to most economically obtain outdoorair :for condenser cooling. A motor driven compressor 22 and a condensercoil 23 are connected to the evaporator coil to form a conventionalrefrigeration system, such as shown in the A. B. Newton Patent2,214,700. The pipe connections of the refrigeration system are tracedas follows: from evaporator 11, a suction pipe 23, motor compressor 22,a pipe 24, condenser coil 23, a pipe 25, a valve 30, and back to coil11. Upon the energization of motor compressor 22, refrigerant is pumpedinto condenser 23, and as the heat is removed from the compressed gas byair circulating through condenser 23 under the power of fan 31, therefrigerant condenses to a liquid to flow through pipe 25 into coil 11when valve is opened.

A relay or contactor 32 ha an energization winding 33 and a pair ofnormally open switches 34- and 35. Switches 34 and 35 close anenergization circuit [for motor compressor 22 whenever relay 32 isenergized. A conventional current overload or abnormal conditionresponsive switch provides an open circuit between terminals 41 and 42whenever the current passing through the circuit of conductors 43 and 44exceeds some predetermined value. Current overload switch 40 isconnected inthe power supply circuit for compressor 22 as follows: froma source of power 4 5, a conductor 5%, switch 35, conductor 43;conductor 44, motor compressor 22, a conductor 51, switch 34, and backto the source of power through a conductor 52. Fan motor 31 is connectedin parallel with motor compressor 22 to be simultaneously energized. Ahigh pressure cutout switch 76 is connected ahead of the condenser 23 bya conduit 77. This switch provides an open circuit between terminals 78and 79 if a pressure above some predetermined value should occur in pipe25.

An impedance relay 53 has an energization winding 54 and a normallyclosed switch 55. Relay 53 is energized and locks out the motorcontactor 32 upon the opening of current overload switch 4th or highrefrigerant pressure limit switch 76. A momentarily open circuit or widegap relay means '60 has an energization winding 61. Relay 61 has aswitch 62 which is made up of contacts '63 and 64 and a movable member'65 moved between the two contacts upon the energization orde-energization of relay 60. While there are other forms of a wide gapor momentarily open switch means, relay 60 provides a momentarily opencircuit whenever the relay means is either dc-energized or energized.

A low pressure cut-off switch 70 is connected by a pipe 71 to'suctionline 23. Switch 70 provides an open circuit between terminals 72 and 73whenever the pressure in suction line 23 reaches some predetermined lowvalue. Low pressure cut-off switches of this type have been used tocontrol motor compressors for a number of years. One particular switchof this type is shown in the Kronmiller Patent 2,377,503.

The energization circuit of relay 32 is traced as follows: from sourceof power 45, a conductor 74, terminal 72, terminal 73, a conductor St),winding 33, a terminal 81, winding 54, switch 62, and back to the sourceof power through a conductor 82. The connection through switch 62 ismade by connecting contacts 63 and 64 together so a circuit existseither between contact 63 and member 65 or between contact 64- andmember 65 depending on whether relay so is energized or de-energized,respectively. A shunt circuit made up of a series connection of switch55, overload switch 40 and high pressure switch '76 is connected betweenterminal 81 and conductor 82 and can be traced by the following circuit:from terminal 81, switch 55, terminal 41, terminal 42, terminal 73,terminal 7% and back to conductor 82.

The energization circuit for valve 30 is traced as follows: from sourceof power 45 through conductor '74, a conductor 83, switch 84, valve 30,conductor 35, and terminal 81. Valve 30 is of a conventional solenoidtype to provide an open passage in pipe to allow refrigerant to flow tocoil 11 whenever the valve is en ergized.

The space or room thermostat 90 has a bimetal operated switch 91. Theswitch 91 is connected to control the energization of relay 92 by acircuit traced as follows: from a secondary winding 93 of a transformer94, a conductor Q5, bimetal 1% and contact 11 which forms switch 91,conductor 162, an energization winding 103 of relay 92, conductor 1%,and back tothe source of power through conductor 165. Upon closingswitch 91, energization winding 103 energizes the relay to close switch84 so valve is energized and coil 11 is cooled to initiate the deliveryof cold air to space 10. Relay 60 can be energized through a circuittraced as follows: from secondary 93, conductor 195, conductor 110,winding 61, a conductor 111, a reset switch 112 located remotely fromthe refrigeration apparatus 21 such as in thermostat 90, a conductor113, conductor 95, and back to the source of power. When switch 112 isclosed or opened, relay 60 is energized or de-energized, respectively,tomomentarily break switch 62 which is connected in the energizationcircuit of relay 53.

Referring to FIGURE 2, the control circuit for the refrigerationapparatus is shown in a more simplified manner. The circuit is readilyrecognized to be quite similar to the high impedance control circuitdescribed in some detail in the Mobarry Patent 2,898,746. The highimpedance circuit which is commonly known in the air conditioning fieldmakes use of two relay windings connected in series. When a shuntcircuit is removed from one of the relay windings and the two areconnected in series, the current is cut down below the current needed tomaintain the energization of the other or main control relay. Before themain control relay and the refrigeration apparatus can be placed back inoperation, the circuit of the impedance relay must be broken and a shuntcircuit re-established around the high impedance relay. Referring toFIGURE 2, winding 54 is the high impedance winding. Upon theenergization of the circuit by the closing of the low pressure switch70, the control relay or contactor 33 is energized to bring about theenergization of motor compressor 22 as shown in FIGURE 1. Theenergization of winding 33 is accomplished through a circuit comprisingthe normally closed switch 55 and the overload switch and high pressurelimit switch 76. Upon a call for cooling the space thermostat, switch 84is closed to energize valve 30 which would cause an increase in thepressure of the suction line 23 to cause switch 70 to close to energizerelay 33 as previously mentioned. As long as no abnormal conditions comeabout, the motor compressor 22 will continue to cycle to maintain thesuction pressure at a level selected by switch 70, and as cooling isrequired in space 10, valve 30 will be opened when the thermostat callsfor cooling and switch 84 is closed.

Upon the presence of an abnormal condition to open switch 40 and/orswitch 76, the energization circuit of winding 33 is then transferred tothe circuit made up of winding and switch 62. Winding 54 has animpedance large enough to reduce the current in this circuit to a valuewhich would not maintain the energization of relay 32. When winding 54is energized, switch opens so that even though the abnormal condition oroverload switch 4- subsequently closes, the current level in winding 33cannot be increased through the previously mentioned shunt circuit tobring about energization of relay 32. Not-or compressor 22 then remainsde-energized until the homeowner or occupant of space 10 discovers thenon-operating condition of the refrigerating apparatus. To reset thesystem and resore the shunt circuit so winding 33 can receive enoughcurrent to energize relay 32, switch 112 must be closed to operateswitch 62. Upon the energization of relay 6%, member as shown in FIGURE1 moves from contact 64 to contact 63; however, during this operation,the wide gap or momentarily open switch 62 breaks the energizationcircuit for winding 54 of relay 53 to close switch 55. Winding 33 isthen energized through the shunt circuit made up of switch 55 andswitches 49 and '76, and the level of current through the winding issufficient to energize relay 32 to re-establish normal operation of therefrigeration apparatus. The resetting operation can be accomplished byopening switch 112 if it had been closed as long as switch 62momentarily opens the energization circuit for winding 54.

In air conditioning apparatuses of this type which are used in domesticdwellings as well as other applications, the safety of the homeownersoften depends on the proper operation of the apparatus; therefore, forthe homeowners protection, apparatuses of this type must pass theUnderwriters Laboratory requirements. One of the provisions of theUnderwriters Laboratories which applies to reset circuits of this typerequires that the system cannot be placed in an unsafe condition whenthe circuit used to provide the resetting action is either shorted oropened. Where low voltage wiring is used and the wires are not protectedfrom mechanical damage, a shorting or breaking of the wires couldpossibly exist. To protect the homeowner from any condition whatever itmight be which would bring about a short or open in the resettingcircuit, Underwriters Laboratory requires that the safety of the circuitshould not be in any way impaired by the presence of a short or open inthe circuit connected to the remote reset switch 112.

By the use of the momentarily open or wide gap switch 62, the resettingoperation for the high impedance reset circuit is obtained from a remoteswitch. By means of the momentarily open switch 62, under no conditioncan the circuit be held open to take the impedance relay winding 54completely out of the circuit so that it can no longer provide the lowcurrent path for winding 33. If the wires leading to switch 112 arebroken or if the switch 112 is jammed shut by the occupant, switch 62would be closed, and upon the presence of an abnormal condition to openswitch 4d, the system or refrigeration apparatus 21 would becomeinoperative and a serviceman would have to be called before coolingcould be obtained.

The importance of the momentarily open switch 62 which can be controlledfrom a remote position contributes to a safety circuit for arefrigeration apparatus using the pump-down method of operation whichcould not be otherwise used since a normal resetting system where thesytem is reset by momentarily opening thermostat switch 91 as shown inthe Mobarry patent is not possible.

While the present invention has been described as applying to oneparticular system, the scope of the present invention is intended to belimited by the following claims in which I claim:

1. In an air conditioning control system, an evaporator coil mounted inan air stream for delivering cooled air to a space, a remote motorcompressor unit, valve means having an energization winding, meansincluding said valve means connecting said compressor to said evaporatorto form a refrigeration system to cool said evaporator when said valveis energized, a low pressure responsive switch means connected to saidrefrigeration system to be responsive to suction pressure of thecompressor, switch means providing an open circuit when said suctionpressure is reduced to said predetermined low value, a source of power,a current overload switch means for providing an open circuit when anexcessive current fiows through a current responsive circuit, a controlrelay having an energization winding and being adapted to connect saidmotor compressor to said source of power through said responsivecircuit, a first relay having an energization winding and a normallyclosed switch, a remotely controlled reset relay having a normallyclosed switch and a normally open switch, said relay insuring a closedcircuit when said reset relay is either energized or de-energized,circuit means connecting said switch of said pressure control, saidcontrol relay energization winding, said first relay energizationwinding and a parallel connection of said reset switches in series tosaid source of power, space temperature responsive switch means, meansincluding said space switch means for connecting said valve energizationwinding to said source of power where upon a call fior cooling in saidspace said valve is energized and said evaporator is cooled by saidrefrigeration system, abnormal refrigeration operating condition switchmeans having an open circuit when an abnormal condition is present,circuit means connecting said condition switch means and said firstrelay switch in a series connection in parallel with said first relayenergization winding and said parallel connection of said resetswitches, said reset relay switches having a wide operating gap suchthat said closed switch opens before said open switch closes uponenergization or deenergization of said reset relay, said reset relayproviding for normal operation of said control system upon an abnormalcondition occurring to open said abnormal condition switch means aftersaid first relay has become energized and said abnormal condition hasdisappeared to close said abnormal condition switch means.

2. A control circuit for controlling the operation of an electric motordriving a refrigeration compressor in an air conditioning installation,a source of power, first relay means having a first energizationwinding, means connecting said relay means to control said motor, secondrelay means having a second energization winding and a normally closedswitch, first switch means comprising a normallyopen and a normallyclosed set of contacts connected in a parallel circuit, said sets ofcontacts being of the wide gap type so that upon operation of saidswitch means said parallel circuit is first momentarily open and theninsuring that said parallel circuit has one set of contacts normallyclosed, circuit means connecting said first energization winding, saidsecond energization winding, and said first switch means in series tosaid source of power, said first and second windings having impedanceswhich limit the current in said circuit below a level required tomaintain 'said first relay energized, abnormal operating conditionresponsive switch means providing an open circuit when an abnormaloperating condition exists in the operation of said air conditioninginstallation, circuit means connecting said normally closed switch meansand said condition responsive switch means in a second series circuit inparallel with a series circuit of Said second winding and said firstswitch means, said second series circuit providing a lower impedanceenergization circuit for said first relay means to energize said firstrelay means whereby upon said abnormal switch means opening said secondseries circuit said second relay is energized to maintain said firstrelay means inoperative even though said abnormal switch meanssubsequently closes until said first switch means is momentarily openedto close said normally closed switch.

3. A control circuit for an electric motor comprising, a source ofpower, first relay means having a first energizing winding, said firstrelay means controlling the operation of said motor, second relay meanshaving a second energization winding and a normally closed switch,abnormal operating condition responsive switch means providing an opencircuit as long as an abnormal operating condition exists, second switchmeans for providing a momentary open circuit and a normally closedcircuit upon each operation, circuit means connecting said firstenergization winding, said second energization and said second switchmeans in a series circuit to said source of power, said series circuithaving a current below the normal operating current of said first relaymeans, circuit means connecting said normally closed switch means andsaid abnormal condition responsive switch means in a shunt circuit inparallel with said second relay means and said second switch meanswhereby a lower resistance path is provided to increase the current insaid first relay means to said normal operating current, said seriescircuit being connected in said circuit and energized when said shuntcircuit is broken upon the presence of an abnormal condition and uponsaid second switch means being operated to momentarily open said seriescircuit after said abnormal switch means closes said low resistancecircuit is again established to bring about energization of said firstrelay means and operation of said motor.

4. A control circuit for an electric motor comprising, a source ofpower, first relay means having a first energizing winding, said firstrelay means controlling the operation of said motor, second relay meanshaving a second energization winding and a normally closed switch,abnormal operating condition responsive switch means proving an opencircuit as long as an abnormal operating condition exists, second switchmeans for providing a momentary open circuit when a switch actuator isoperated, circuit means connecting said first energization winding, saidsecond energization and said second switch means in a series circuit tosaid source of power, said series circuit having a current below thenormal operating current of said first relay means, circuit meansconnecting said normally closed switch means and said abnormal conditionresponsive switch means in a shunt circuit in parallel with said secondrelay means and said second switch means whereby a lower resistance pathis provided to increase the current in said first relay means to saidnormal operating current, said series circuit being energized when saidshunt circuit is broken upon the presence of an abnormal condition andupon said second switch means being operated after said abnormal switchmeans closes said low resistance circuit is again established to bringabout operation of said motor.

References Cited in the file of this patent UNITED STATES PATENTS2,891,386 Winter June 23, 1959 2,898,746 Mobarry Aug. 11, 1959'2,986,018 Algren May 30, 1961 3,022,641 Myck Feb. 27, 1962

1. IN AN AIR CONDITIONING CONTROL SYSTEM, AN EVAPORATOR COIL MOUNTED INAN AIR STREAM FOR DELIVERING COOLED AIR TO A SPACE, A REMOTE MOTORCOMPRESSOR UNIT, VALVE MEANS HAVING AN ENERGIZATION WINDING, MEANSINCLUDING SAID VALVE MEANS CONNECTING SAID COMPRESSOR TO SAID EVAPORATORTO FORM A REFRIGERATION SYSTEM TO COOL SAID EVAPORATOR WHEN SAID VALVEIS ENERGIZED, A LOW PRESSURE RESPONSIVE SWITCH MEANS CONNECTED TO SAIDREFRIGERATION SYSTEM TO BE RESPONSIVE TO SUCTION PRESSURE OF THECOMPRESSOR, SWITCH MEANS PROVIDING AN OPEN CIRCUIT WHEN SAID SUCTIONPRESSURE IS REDUCED TO SAID PREDETERMINED LOW VALUE, A SOURCE OF POWER,A CURRENT OVERLOAD SWITCH MEANS FOR PROVIDING AN OPEN CIRCUIT WHEN ANEXCESSIVE CURRENT FLOWS THROUGH A CURRENT RESPONSIVE CIRCUIT, A CONTROLRELAY HAVING AN ENERGIZATION WINDING AND BEING ADAPTED TO CONNECT SAIDMOTOR COMPRESSOR TO SAID SOURCE OF POWER THROUGH SAID RESPONSIVECIRCUIT, A FIRST RELAY HAVING AN ENERGIZATION WINDING AND A NORMALLYCLOSED SWITCH, A REMOTELY CONTROLLED RESET RELAY HAVING A NORMALLYCLOSED SWITCH AND A NORMALLY OPEN SWITCH, SAID RELAY INSURING A CLOSEDCIRCUIT WHEN SAID RESET RELAY IS EITHER ENERGIZED OR DE-ENERGIZED,CIRCUIT MEANS CONNECTING SAID SWITCH OF SAID PRESSURE CONTROL, SAIDCONTROL RELAY ENERGIZATION WINDING, SAID FIRST RELAY ENERGIZATIONWINDING AND A PARALLEL CONNECTION OF SAID RESET SWITCHES IN SERIES TOSAID SOURCE OF POWER, SPACE TEMPERATURE RESPONSIVE SWITCH MEANS, MEANSINCLUDING SAID SPACE SWITCH MEANS FOR CONNECTING SAID VALVE ENERGIZATIONWINDING TO SAID SOURCE OF POWER WHERE UPON A CALL FOR COOLING IN SAIDSPACE SAID VALVE IS ENERGIZED AND SAID EVAPORATOR IS COOLED BY SAIDREFRIGERATION SYSTEM, ABNORMAL REFRIGERATION OPERATING CONDITION SWITCHMEANS HAVING AN OPEN CIRCUIT WHEN AN ABNORMAL CONDITION IS PRESENT,CIRCUIT MEANS CONNECTING SAID CONDITION SWITCH MEANS AND SAID FIRSTRELAY SWITCH IN A SERIES CONNECTION IN PARALLEL WITH SAID FIRST RELAYENERGIZATION WINDING AND SAID PARALLEL CONNECTION OF SAID RESETSWITCHES, SAID RESET RELAY SWITCHES HAVING A WIDE OPERATING GAP SUCHTHAT SAID CLOSED SWITCH OPENS BEFORE SAID OPEN SWITCH CLOSES UPONENERGIZATION OR DEENERGIZATION OF SAID RESET RELAY, SAID RESET RELAYPROVIDING FOR NORMAL OPERATION OF SAID CONTROL SYSTEM UPON AN ABNORMALCONDITION OCCURRING TO OPEN SAID ABNORMAL CONDITION SWITCH MEANS AFTERSAID FIRST RELAY HAS BECOME ENERGIZED AND SAID ABNORMAL CONDITION HASDISAPPEARED TO CLOSE SAID ABNORMAL CONDITION SWITCH MEANS.